The p53 gene family although small in number, plays important roles in cells and whole animals. p53 itself is[unreadable] a major tumor suppressor that integrates multiple sources of stress with cellular response including arrest,[unreadable] senescence and apoptosis. The p53 homologues p63 and p73 are critical for development based on the[unreadable] phenotype of mice lacking either of these genes, and they may also contribute to tumor suppression. The[unreadable] goal of this project is to understand how p53 members are regulated by previously identified or newly[unreadable] discovered cellular factors and how they interact with each other and with DNA. Aim 1 of this project will[unreadable] focus on the checkpoint kinases Chk1 and Chk2. It will elucidate the structure and function of Chk2 with[unreadable] respect to novel Chk2 phosphorylation sites, Chk2 substrate specificity and interaction with its substrates[unreadable] such as p53. The finding that both Chk kinases through E2F1 control p73 induction after DNA damage will[unreadable] be pursued to elucidate how E2F stability and activity are targeted by Chk1 and Chk2. Whether and how[unreadable] oncogenes abrogate the ability of Chk2 to affect p53 activity will be determined in collaboration with Scott[unreadable] Lowe. With Carlos Cordon-Cardo the properties of newly identified tumor-related Chk2 mutations will be[unreadable] analyzed. The goal of Aim 2 is to identify and characterize proteins that interact with different isoforms of[unreadable] p63. The possible effect of p63 on newly identified proteins will be tested and conversely the effect of new[unreadable] binding partners on p63 activities will be determined. Aim 3 will consist of experiments examining the[unreadable] interactions of p63 and p73 with mutant p53 and with DNA. First, small molecules that can disrupt the[unreadable] interaction between mutant p53 proteins and p63 or p73 will be identified and the cellular outcome of such[unreadable] compounds will be determined. Second, the optimum DNA binding sequences for p63 and p73 isoforms in[unreadable] vitro and in vivo will be determined, and with Arnold Levine an informatics approach will be taken to identify[unreadable] human genes that may be preferentially regulated by these p53 family members.